1. Field of the Invention
The present invention relates to an image display apparatus using electron emitting elements.
2. Related Background Art
In a flat panel display where a large number of electron emitting elements as an electron source are arranged on a flat substrate, and a phosphor as an image forming member on an opposing substrate is irradiated with electron beams emitted from the electron source, thereby making the phosphor body emit light to display an image, it is necessary to maintain under high vacuum the inside of a vacuum container having therein the electron source and the image forming member. The reason is that, if gas is produced and the pressure is increased within the vacuum container, the electron source is adversely affected depending on the kind of the gas to decrease the amount of emitted electrons and a bright image can not be displayed.
In particular, it is a characteristic problem in a flat panel display that gas produced from the image display member accumulates around the electron source before the gas reaches a getter provided outside an image display area, leading to local pressure increase and associated deterioration of the electron source. Japanese Patent Application Laid-open No. H09-082245 describes a getter provided in an image display area for instantaneously absorbing produced gas to suppress deterioration and breakage of the elements. Japanese Patent Application Laid-open No. 2000-133136 describes a structure where a non-evaporable getter is provided in an image display area while an evaporable getter is provided outside the image display area. Further, as described in Japanese Patent Application Laid-open No. 2000-315458, a method is also devised where degasing, forming of a getter, and seal bonding (to form a vacuum container) are conducted in a series of operations.
Getters can be broken down into evaporable getters and non-evaporable getters. An evaporable getter can absorb water and oxygen at an extremely high speed while both an evaporable getter and a non-evaporable getter can absorb almost no inert gas such as argon (Ar). Argon gas is ionized into plus ions by electron beams. The plus ions are accelerated by an electric field for accelerating electrons and are bombarded onto the electron source, thereby damaging the electron source. Further, in some cases, electric discharge is caused inside, which can break the apparatus.
On the other hand, Japanese Patent Application Laid-open No. H05-121012 describes a method for maintaining high vacuum for a long time by connecting a sputter ion pump to a vacuum container of a flat panel display. However, a method of driving an ion pump suitable for use in an image display apparatus and a structure of the same are not described therein.